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New Fluke
My old meter died yesterday, boss baught me a new Fluke 116 true RMS meter.
I've been playing with it all day. Interesting observances around the house: 59.99 hz on the outlet in the kitchen 122.8 volts What I thought was interesting is 60.00hz from ground to water pipe. Note: water pipe is not bonded to the service panel. Panel has its own ground rod. However netural is connected to the ground bar in this panel, I guess that's where the signal is coming from. 0.412 volts from ground to water pipe Continuity of about 14 million ohms from ground to water pipe. Thought this interesting too since there is no obvious connection between the two, other than the dirt that separates them, it has however been raining for the last 2 days. And when I say water pipe, I mean the brass valve body of a shut off. My pipes are CPVC. Temperature inside is 72.3 degrees. Just some odd ball stuff I was messing with this evening. |
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You are very nit-picky. A frequency of .001 Hertz can be attributed to the tolerance of your measuring device or more likely a variation in the power provided by the local utility. 0.412 volts from ground to water pipe is not an unusual reading. Be glad there is 14 MegOhms from ground to wter pipe. The human body is a 1 MegOhm resistor. Measure that between your hands. No, it will not read exactly 1,000,000 ohms. Now grab your calculator. Divide 1 by .003. Divide that answer by .003. Continue this process until you come to a very interesting answer. Our numbering system is the base 10 system which uses the numerals 0-9. 3 is the square root of nine. Think about this & stay away from electricity. |
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Andrew, Personally, I would chase freqs with a scope, not a hand held anything. Although the unit you have seems fairly accurate, but then Fluke does have it reputation to defend. I hope you get the benefit of a lecture from TK regarding the use of "Ground Rods" in residential wiring. Using the correct terms, define the "EGC" vs the Ground Rod. Bonding of the Neutral Conductor and earth ground must occur at the main panel. Why is the "EGC" different from the Neutral Conductor. Have at it, TK sent me back to the code book to get that information accurately stored in my blockhead. :) |
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I say, we just make this into an educational thread.
TK: Please fill us in about the ground rod and it's purpose. Last night I googled the subject, but all I found was sites "selling ground rods". Not much in the way of there exact purpose. I did find a little about ground rods for HAM radio operators, but I feel that didn't pertain to what I was researching. As far as my readings... I was just messing around with it, exploring some of it's newer features that my old meter didn't have. I wasn't actually troubleshooting any particular problem. You are correct about the human body, although the exact measurment eludes me, but I think you were pretty close to what I got.
Bonding of the Neutral Conductor and earth ground must occur at the main panel. Why is the "EGC" different from the Neutral Conductor.
After the recent discussions about the ground rod, last night I went out to try to find mine. Now I know when I first moved in this house, there was a rod sticking out about an inch. I nicked it with the lawnmower. But last night I couldn't remember where it was at. All I saw was the ground wire coming out of the basement wall, and going into the ground. I would have investigated further, but it was dark, drizzling, and I was in m PJ's, so I just called it a night, but I know it's there somewhere, it has just gotten buried under some tall grass or something. But I'm very interested to know all you all are willing to tell me about the ground rod. As many people here have stated that it is not used for what most people think it is used for, but nobody (that I have seen) has explained exactly what it's purpose is. |
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I can say that a few years back, I used to pick up an AM radio station on my phone line, quite clear. My house didn't have an interface box, just a porcelain... thing... with two connectors, and some kind of black dail that the telephone was hooked to. The phone company came in and put in a modern interface box and grounded the box via a connection to the breaker panels ground wire. The problem of AM radio in the phone went away! And then Direct TV hooked their system to the ground wire, then the old comcast cable ground hooks to it. There's a lot of stuff on that rod! |
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The best thing I found on the internet is:
https://www.nachi.org/forum/f27/2-12...17/index5.html
No the voltage takes ALL paths of resistance... it is proportinally greater on the least resistive path but in fact it takes all paths.
You are confusing logic... you are saying... Paul since the Grounding Electrode Conductor is attached in the panel anyway... and the Grounded conductor is the path back... why need the EGC... is that not what you are beating around the BUSH to really ask? The earth is a weak.. very weak conductor at best... are you going against conventional logic as to why the fault current would travel back on the grounded conductor to clear a fault versus on the earth... this can be done simply via OHMS law. The EGC lets say in that " POWER" took will take any voltage from Line to Ground and remove it via a low impedance path back to the source... allowing the OCPD to fulfill its function... the earth could not provide this function... do the math on a 25 OHM ground rod... 120V into 25 OHMS = 4.8A... do you think this would clear the fault? The connection to ground helps to give zero potential but not to clear any faults.....the ground rod in itselfs function is for lightning, Transiant voltage and surge voltage. Because the way I've got this figured, if you had 25 ohms to ground on the ground rod, them applying 120 volts to this would run a hair under 5 amps. However, since the ground is bonded to the netural in the service box, then any fault to ground, would most likley trip a circuit breaker due to a fault to netural, rather than to ground, er the netural would be the first at "fault", as it would provide more of a dead short than that of a regular "earthed" ground. Perhaps I'm way off, I'm just trying to understand all this. |
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Learning learning learning, never stop learning.
Mark: I played a smooth card to obtain this new fluke. A couple of weeks ago, I nicked the meter leads on my old meter. And the boss purchased a new set of $50 meter leads for the old fluke. Then, when the old fluke bit the dust, where as the rest of the company was going with a "cheaper name" I made the comment that these new leads would only work on a fluke, and it would be better to replace the meter with another fluke. I don't know if that's actually true, but the plan worked, and in my truck is a brand new fluke meter. |
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Andrew,
I got my Tech hand held two probe scope by similar logic. I had to keep borrowing the Dev. Labs portable scope for business trips. Eventually I built a case for needing my own. When I retired, my boss let this device be packed in with my debris and shipped home. No one else needed it or knew how to use within the input ports to our printers. :) The best source for this information is the NEC Code Book. The grounding rod is used to carry lighting strikes safely to earth ground. The bare wire ground used inside the residence is used to set up a very low impedance between the Hot conductor and ground. Its purpose is to take a high degree of current away from the Circuit Breaker. Because of the outflow of current, the Circuit Breaker causing the breaker to trip. |
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 Originally Posted by andrewc...
The Earth itself has a gradient of voltage across it, particularly during a lightning storm. You really don't want to touch your sink and your stove and get a shock. Neither do you want to get a shock from your plumbing system or swimming pools. Swimming pools are a very special case. Another use of this ground is for communications. What? The coax of your cable TV is grounded. The TV is too, likely through the polorized cord. Ground may also be the way in which USB devices communicate with each other. There are typically 4 pins, +5, ground and 2 communcation pins. That ground is a reference. The ground rod also provides a 0 volt reference for you to measure from. So, you get at least 3 purposes for the ground rod 1. lightning 2. equipotential bonding - shocks 3. provides a reference potential Ground - link in the outlets 1. provides insulation protection 2. Provides a reference 3. Provides a path to divert fault currents from line filters, transients, surge suppression 4. Connects devices such as a washer to "zero potential" 5. Provides a path of communications (CATV, computers) |
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Good information. Thanks guys.
2. equipotential bonding - shocks
For instance, in my work, when a wire burns off an element or something and touches the inside of the cook top, rather than have 120 volts of standing current sitting on the stove itself shocking everybody, it faults to the ground and trips the breaker. I'd write more, but I slashed my index finger pretty good at work today and it's a litte sore, typing is difficult. Learning learning.. lesson for the day, be mindful of where your hand is at when trying to pull a filter drier off a reach in, it popped off and my finger went right across the corner of the sheet metal box. |
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This link backs up what I said: Cabling Installation & Maintenance - Ground potentials and damage to LAN equipment |
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Even though this deals with substation faults, you can extrapolate this somewhat to what happens with a lightning strike:
Earth potential rise - Wikipedia, the free encyclopedia |
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Additional question...
In the next few years I'm planning to have a metal roof installed, on some houses I have seen 3 or 4 lightning rods connected to the metal roof, then connected to a ground rod I assume. Should this be done? And if so, should it be grounded to the service ground rod, or it's own ground rod. I have only seen these from the road, and never close enough to really see where exactly it grounds to. What ever is done up there will be done by a contractor, I despise heights, and Andrew "don't do roof's" period! |
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I'm no lightning expert, but... Lightning rods have points, which means lightning is attracted to the point. It has a very high concentration in terms of volts per area. Thus the lightning is attracted to the rods rather than the roof. I would think it should go to the service ground. They may have to use multiple rods to make up the ground. Fundamentals of Lightning Protection - National Lightning Safety Institute Lightning rod - Wikipedia, the free encyclopedia |
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